∫x^23^xdx
=(1/ln3)∫x^2d3^x
=(1/ln3)[x^23^x-∫2x3^xdx]
=(1/ln3)[x^23^x-(1/ln3)∫2xd3^x]
=(1/ln3)[x^23^x-(1/ln3)(2x3^x-(2/ln3)3^x]+C